10.2. Antibiotics
A subsection of Biology, 9700, through 10. Infectious diseases
Listing 10 of 82 questions
Use Three different strains, A, B and C, of a species of bacterium were grown on nutrient agar in a divided petri dish until they formed ‘lawns’ covering the agar. Three discs of filter paper were soaked in a solution of a penicillin antibiotic and one disc placed in contact with each of the bacterial strains for 10 minutes. After 24 hours, zones of clearance, indicating bacterial cell death, were seen in the ‘lawns’ of strains A and B. The appearance of the petri dish 24 hours after addition of antibiotic is shown in . zone of clearance zone of clearance ‘lawn’ of bacteria growing on nutrient agar position where disc of filter paper soaked in antibiotic had been placed strain A strain B strain C The effectiveness of the antibiotic is proportional to the area of the zone of clearance. Measure the diameters of each of the zones of clearance of bacterial strains A and B and record them to the nearest mm in Table 3.1. Using r2, calculate the area in mm2 of the zone of clearance for each strain of bacterium and record them in Table 3.1. Calculate the ratio of the area for strain A to the area for strain B and record the ratio in Table 3.1. Table 3.1 bacterial strain A B diameter of zone of clearance / mm area of the zone of clearance / mm2 area for strain A : area for strain B Examiner’s Use Explain the different effects of the antibiotic on bacterial strains A, B and C. Describe the role of natural selection in the spread of bacterial strains, such as A and B, when an antibiotic is used. The β-lactam antibiotics, such as penicillin, are similar shaped molecules to the substrate of a bacterial enzyme, transpeptidase. Explain the mode of action of β-lactam antibiotics on susceptible bacteria.
9700_s07_qp_4
THEORY
2007
Paper 4, Variant 0
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The fungus Penicillium chrysogenum is grown in fermenters on an industrial scale to produce penicillin, using a batch culture system. Explain why batch culture, rather than continuous culture, is used for the production of penicillin. Temperature and pH are normally controlled in the fermenter. Temperature is kept constant, while pH is held at a value of 5.5 for the first stage of the fermentation and then raised to 6.8 and kept constant for the remainder of the fermentation period. shows how the pH and the concentration of penicillin in the culture change over time, when the pH is controlled and when the pH is not controlled. time / hours pH penicillin concentration / arbitrary units Key pH controlled pH not controlled Key pH controlled pH not controlled With reference to , describe and explain the differences in the concentration of penicillin in the culture when the pH is controlled and when the pH is not controlled. Explain why penicillin affects bacteria but not viruses.
9700_s09_qp_4
THEORY
2009
Paper 4, Variant 0
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The sensitivity of bacteria to antibiotics can be tested using the disc diffusion method. An inoculum of the bacteria is spread onto agar culture plates and then filter paper discs impregnated with antibiotic are pressed onto the surface of the agar. The plates are incubated. Bacteria grow as a ‘lawn’ across the agar, but a circular zone (the zone of inhibition) appears around any disc where bacterial growth is inhibited. Two species of bacteria, A and B, were grown on separate culture plates in the presence of three types of filter paper disc: 1 – no antibiotic 2 – penicillin V, a natural penicillin 3 – carboxypenicillin, a synthetic penicillin. The appearance of the incubated plates is shown in . bacterium A bacterium B With reference to , explain the effect of penicillin V on bacterium A. Bacteria A and B have different outer layers, as shown in . bacterium A cell surface membrane peptidoglycan wall outer membrane bacterium B With reference to and describe how the outer layers of bacterium B differ from those of bacterium A explain the different effects of penicillin V on bacteria A and B suggest how the synthetic penicillin, carboxypenicillin, is able to affect the growth of bacterium B. Distinguish between batch culture and continuous culture of microorganisms. Explain why batch culture rather than continuous culture is used in the production of penicillin.
9700_s10_qp_42
THEORY
2010
Paper 4, Variant 2
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The sensitivity of bacteria to antibiotics can be tested using the disc diffusion method. An inoculum of the bacteria is spread onto agar culture plates and then filter paper discs impregnated with antibiotic are pressed onto the surface of the agar. The plates are incubated. Bacteria grow as a ‘lawn’ across the agar, but a circular zone (the zone of inhibition) appears around any disc where bacterial growth is inhibited. Two species of bacteria, A and B, were grown on separate culture plates in the presence of three types of filter paper disc: 1 – no antibiotic 2 – penicillin V, a natural penicillin 3 – carboxypenicillin, a synthetic penicillin. The appearance of the incubated plates is shown in . bacterium A bacterium B With reference to , explain the effect of penicillin V on bacterium A. Bacteria A and B have different outer layers, as shown in . bacterium A cell surface membrane peptidoglycan wall outer membrane bacterium B With reference to and describe how the outer layers of bacterium B differ from those of bacterium A explain the different effects of penicillin V on bacteria A and B suggest how the synthetic penicillin, carboxypenicillin, is able to affect the growth of bacterium B. Distinguish between batch culture and continuous culture of microorganisms. Explain why batch culture rather than continuous culture is used in the production of penicillin.
9700_s10_qp_43
THEORY
2010
Paper 4, Variant 3
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The diagram shows one way of testing the effect of an antibiotic on bacteria. petri dish with nutrient agar containing bacteria disc of filter paper soaked in antibiotic colonies of bacteria grown for 5 weeks diameter of zone measured every week for 5 weeks The table shows the results of testing five different types of bacteria. Zones of less than 13 mm show the presence of resistant bacteria. diameter of zone / mm type of bacteria week 1 week 2 week 3 week 4 week 5 24.10 21.90 19.00 17.60 14.30 18.60 15.40 12.20 9.00 0.00 17.90 12.80 12.40 11.10 10.90 19.40 15.30 13.20 8.10 0.00 22.00 21.00 20.50 20.40 20.40 Which statement can be supported by this data?
9700_s11_qp_11
MCQ
2011
Paper 1, Variant 1
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The diagram shows one way of testing the effect of an antibiotic on bacteria. petri dish with nutrient agar containing bacteria disc of filter paper soaked in antibiotic colonies of bacteria grown for 5 weeks diameter of zone measured every week for 5 weeks The table shows the results of testing five different types of bacteria. Zones of less than 13 mm show the presence of resistant bacteria. diameter of zone / mm type of bacteria week 1 week 2 week 3 week 4 week 5 24.10 21.90 19.00 17.60 14.30 18.60 15.40 12.20 9.00 0.00 17.90 12.80 12.40 11.10 10.90 19.40 15.30 13.20 8.10 0.00 22.00 21.00 20.50 20.40 20.40 Which statement can be supported by this data?
9700_s11_qp_13
MCQ
2011
Paper 1, Variant 3
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Tuberculosis (TB) is an infectious disease that kills about three million people worldwide each year. Name the pathogenic organism that causes tuberculosis. is a transmission electron micrograph of the organism that causes tuberculosis. X Y The actual length of the cell between X and Y in is 2 µm. Calculate the magnification of the electron micrograph. Show your working and give your answer to the nearest whole number. magnification × The organism that causes tuberculosis is a prokaryote. State three features of prokaryotes. 1. 2. 3. In the 1940s, the use of antibiotics led to a steady decrease in the number of new cases of tuberculosis. However, in many developed countries, the number of new cases stopped decreasing in the mid-1980s and is now increasing. State one factor, other than drug therapy, that contributed to the steady decrease in the number of new cases of tuberculosis. Outline three reasons why, in many developed countries, the number of new cases of tuberculosis is now increasing. 1. 2. 3. Streptomycin was the first antibiotic to be discovered that was effective against the pathogen that causes tuberculosis. Streptomycin causes the death of the pathogen by binding to ribosomes and inhibiting protein synthesis. Suggest two ways in which streptomycin acts at ribosomes to inhibit protein synthesis. 1. 2. Streptomycin does not harm mammalian cells. Suggest an explanation for this.
9700_s11_qp_22
THEORY
2011
Paper 2, Variant 2
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Questions Discovered
82